THE DIFFERENT KINDS OF SEAMS.
There are two kinds of seams proper, viz.: The butt seam and the lap
seam. The butt seam is used principally for joining horizontal waste
pipes and in lengthening traps, or for any purpose where it is desired
not to have the point of junction show. This form of seam can be burned
clear through—that is, the lead can be heated until fusion takes place
nearly through the entire sheet. It is generally necessary to add lead
to the seam if it is desired to make the seam as strong as the sheet it
joins, unless the article to be burned is of such a size as to be
possible to allow of its being burned on both sides, which makes the
strongest of seams. The lead for the butt seams is prepared by rasping
the edges of the lead sheet to be joined straight and true, Fig. 22, so
that when the edges of the lead are brought together they will fit close
its entire length. The edges are then shaved for a distance of ⅛ inch
each side of the edge, making a seam ¼ inch wide. On stock heavier than
12-pound sheets the edge should be shaved off, making a deep V-shaped
groove, and the seams must be made by adding lead. This allows the
fusion to take place nearly through the sheet. The butt seam is the
simplest form to burn, no matter in what position it is placed.
[Illustration:
_Fig. 22.—Rasping the Edges of the Lead Sheet Straight and True._
]
The lap seam is the seam commonly used, and as between the butt seam and
the lap seam the latter is generally to be preferred. As it is not
necessary to cut and trim the edges true, it dispenses with any
additions of lead, except at rare intervals; it leaves the left hand
free to handle the shave hook, and the lap can be dressed to fit any
uneven spots. It also makes the next best seam to through fusing. By lap
seaming a tank can be lined in about half the time required to butt seam
the same article, which is an important item to the customer.
[Illustration:
_Fig. 23.—Burning a Lap Seam._
]
The lead for this form of seam is prepared, as its name indicates, by
lapping one sheet ½ to ¾ inch over the other sheet. The under edges are
to be shaved clean, as also the upper edge. The lead required to make
the seam is melted from the upper lap and is fused on the lower sheet.
There is no reason why the lead at the point of juncture cannot be made
as thick as the original lead. This is the point aimed at in practicing,
and the only accurate way to determine the relative strength of the
seams is to cut squarely across a finished seam, then bend the beam
slightly. The thickness can then be noted. A cross section of a perfect
lap seam is shown at _a_ in Fig. 23. The beginner should practice the
different seams until the thickness of the joint can be told by the
looks of the lead. A few days' diligent practice at the bench will soon
train the eye to note any imperfection that may arise.
The different seams will be taken up serially. A description of how the
seams are prepared and the several positions of the blow pipe, as well
as the little difficulties that may arise, is the extent of the
instruction that can be given. The rest must come with practice and the
application of a little common sense. There is no royal road to this
business; but practice, and practice hard, is the only way to
satisfactorily master the blow pipe and flame, and in practicing
remember that all this work has been done before, and can be easily done
again, _and by you_. Do not get discouraged by failure to make a perfect
seam at the first application, but stick to it for a short time and it
will be found to be a most fascinating pastime, for which the persistent
student will eventually be well repaid.
Flat Butt Seam.
For practicing I would recommend the beginner to use pieces of sheet
lead about 12 inches long, as strips of that length are much easier to
prepare. The edges are straightened with a fine rasp which is held
lengthwise of and parallel to the edge to be trued, in the manner shown
in Fig. 22. The rasp must be used lightly, or it will be apt to tear the
lead and so leave it in worse condition than before using it. The edge
should then be gone over with the shave hook and cleaned. Then shave the
top surface a distance of ⅛ inch each way from the edge, which will make
a seam ¼ inch wide when finished. Then butt the edges together and
secure the sheets firmly to a board with a few tacks. The extra lead
that is necessary to add to make a butt joint full must be obtained from
a strip of lead, which should be about ⅛ inch square and _shaved clean_.
After regulating the flame to the proper size and shape the burning
should be begun at the end of the seam nearest the operator. With the
point of the inner flame melt off a drop from the lead strip and have it
fall squarely on the seam just slightly in advance of the point of
fusion. Follow it up with the flame, placing the point of the inner
flame directly over the edges of the seam, which is almost under the
lead drop. As soon as fusion commences on the lead seam the melted drop
will flow to the bright spot and immediately unite with it. The flame
must then be quickly removed and the drop be allowed to set.
In order to avoid any misunderstanding regarding the time required for
the lead drop to set I would say that the drop will cool immediately
upon the flame being removed from contact with it. It is not necessary
to wait for any specified time, but if the flame is allowed to play
constantly on the sheet it is apt to get overheated, and when in that
condition it takes very little heat to set the lead running like water.
To avoid this the flame should be lifted clear of the seam for an
instant after each drop has been fused into place.
[Illustration:
_Fig. 24.—Burning a Flat Butt Seam._
]
These remarks apply to all seams that are made by the blow pipe process
and should be noted, as this particular point will not be referred to
again. Now melt off another drop and let it fall as before, only it
should lap on the previous drop about one-half its diameter. Secure it
to the seam as before. This operation should be repeated until the seam
is completed, and if the seam is correctly done a section will appear as
_a_ in Fig. 24. This form of flat seam should be practiced until
perfectly familiar with the blow pipe flame and until the beginner can
approach the lead with the flame without burning holes through it, which
will probably be the first thing to happen.
Upright Butt Seam.
The upright butt seam is seldom used on large work, as it is a difficult
matter to make an upright butt seam that will stand the test, as, if a
finished seam is cut into short pieces, an examination of the severed
ends will show many weak places that were previously thought to be very
strong. The reason of this is that the heat necessary to fuse through
the lead will cause the lead to run from the seam and leave a hole.
The sheets for practice are prepared as described for flat butt seams,
and must be securely tacked to a board which can be supported in an
upright position. The burning is begun at the bottom of the seam. The
flame must be shortened considerably, as the fusing must take place
somewhat slower than in flat seams, as in upright or inverted seams the
attraction of gravity remains to be overcome, and the operator must have
plenty of time between the commencement of brightening and the actual
fusing to drive the melting drop to the exact position desired.
[Illustration:
_Fig. 25.—Burning an Upright Butt Seam._
]
The blow pipe is held so that the flame strikes the seam squarely and at
about a right angle with the sheet, as shown in Fig. 25. When fusion
starts the flame should be drawn quickly to one side, and if the lead is
at the proper temperature the melted drop will follow the point of
flame, and as it comes in contact with the adjoining edge it will
properly unite. It is not necessary to add lead to these seams oftener
than at intervals of 5 or 6 inches, or as often as the lead shows signs
of weakening, when it may be added by holding the lead strip against the
lead sheet and slightly above the flame. The melted drop will unite with
the sheet and can then be driven to any desired position. This seam will
show the characteristic beads, but they will lie nearly level with the
lead sheets, and if a scratch cloth be rubbed over the seam all traces
of the position of the seam will be removed.
To make a really strong seam it must be gone over with the flame at
least twice, as after fusion of the edges takes place the flame can be
used quite strong without fear of the lead running from the seam. Do not
leave this seam until you are satisfied that it is nearly perfect. It is
good practice, and every hour spent only makes the mastery of the next
seam come so much more quickly.
Horizontal Butt Seam.
This form of seam cannot be used to any advantage on general work, but,
like seams in other positions, it cannot always be avoided. The practice
sheets are prepared and tacked securely to the board, as previously
described, and are then placed in the position shown in Fig. 26. The
position of the blow pipe is as shown at _a_. The flame should strike
the sheet nearly square. The edge of the upper sheet should be heated
first, and as it brightens the flame should be directed onto the edge of
the lower sheet. If properly done, fusion will at once take place.
[Illustration:
_Fig. 26.—Burning a Horizontal Butt Seam._
]
The object sought is to get a light fusion between the two sheets before
attempting to burn the lead clear through the seam. If this is not done,
the lead will run from the upper sheet and cause holes, or at least will
seriously weaken the upper sheet, as shown in cross section at _b_.
After fusion is once obtained it is a simple matter to go over the seam
a second time, which can then be fused clear through without much danger
of burning holes through the sheet. Lead can be added in the same manner
as in upright seams if necessary.
Inverted Butt Seam.
This seam is used extensively in joining waste pipes which conduct the
acid from tanks to the drain. These pipes are usually in a horizontal
position and the seams must be burned in place. The most difficult part
of the seam is in starting it. When fusion has once taken place the
balance of the seam is easy. The seam is prepared the same as described
for other butt seams. Care must be taken to have the edges butt close.
The board can then be supported in the required position by any
convenient device.
The blow pipe flame must be made as short as possible and still melt the
lead. The point of the inner flame is then placed squarely on the seam.
Both edges must be heated at once. If the edges begin to brighten and do
not show an inclination to fuse, the flame should be drawn quickly to
one side, and the melted drop will follow the point of flame and unite
with the adjoining edge. This seam, in common with the other butt seams,
should be gone over the second time to assure a perfect seam. It is
difficult work to add lead to the flat inverted seam. When necessary to
do so, however, it can be added by burning the end of the lead strip to
the seam. The strip is then melted off, leaving a drop of lead affixed
to the seam, which can then be drawn to the required spot with the
flame.
The characteristic inverted seam shows pits upon examination of the
reverse side of the sheets. These are caused by overheating. The
operator will often be surprised at the inverted butt seam showing a
remarkable fullness. This is accounted for upon the examination above
referred to. The lead, upon the application of the heat, runs from the
upper or back side of the sheet and forms a very full seam. For that
reason the inverted butt seams always appear stronger than they really
are. See inverted lap seam, Fig. 27.
Lap Seams.
The lap seams are the seams commonly used on all classes of work. When
the beginner becomes proficient with the blow pipe no trouble will be
experienced in making lap seams that will show when cut a joint equal in
thickness to the sheets that are joined. The lead sheets for the flat
lap seam are prepared by shaving clean the exposed edge; also, shave the
sheets where they touch each other. The upper edges can then be shaved
for a distance of ⅛ inch each side of the lap, which will make the
finished seam ¾ inch wide, as shown at _a_ in Fig. 23. The sheets should
be lapped ½ to ¾ inch, according to the weight of the stock. It is very
evident that light weights would not require as large a lap as would
heavier sheets, as the object of lapping the sheets is to leave the
sheets practically as one piece, and the lead, to accomplish this
object, is to be melted from the upper sheet.
[Illustration:
_Fig. 27.—Burning an Inverted Lap Seam._
]
From the foregoing it will be seen why a 12-pound sheet requires a
½-inch lap, while a 24-pound sheet would require a ¾-inch lap. The
flame, when regulated to the work, is brought to bear squarely on the
edge of the upper sheet, slanting slightly in the direction of the lower
sheet, as shown. When the edge has brightened almost to the fusing point
the blow pipe should be drawn quickly to one side and from the upper
sheet to the lower sheet. If the metal is sufficiently hot the melted
drop will follow the point of the flame and instantly fuse with the
lower sheet, and if properly done the seam will resemble _b_ in Fig. 23.
This process is repeated, advancing about ⅛ to ¼ inch each time. Do not
attempt to fuse a large surface at a time. Experts cannot do such a
thing satisfactorily, so why should a beginner try to? Rather, try to
fuse small surfaces quickly and strongly, as better work and more of it
can be accomplished in that manner.
Horizontal Lap Seams.
This seam is prepared precisely as described for flat lap seams. The
strips can be fastened to a board with a few tacks. The strips can then
be supported in the position shown in Fig. 28. The burning is commenced,
as before, at the side nearest the operator. The flame must be made as
short as is consistent with the weight of the stock. It will be found to
the beginner's advantage to have fusion take place slowly. The point of
the inner flame is brought to bear on the outer edge of the lapped sheet
and at an angle of 45 degrees. Both sheets should begin to brighten at
about the same time. The melted drop must be driven against the back
sheet by the force of the jet of flame, and if the sheets are clean
fusion will take place quickly.
[Illustration:
_Fig. 28.—Burning a Horizontal Lap Seam._
]
The drops or beads of lead will appear very small on this form of seam,
owing to that great obstacle, gravity, which causes the drop when melted
to flow downward and so swell the seam. The drops, in common with other
forms of lap seams, should be made short, letting each drop overlap the
previous drop as much as possible. Great care must be taken not to
weaken the seam, as shown at _a_. The beginner should strive to get the
seams so that when cut into small sections each section will resemble
the result shown at _b_.
Upright Lap Seams.
Prepare the sheets as for flat lap seams, fastening the sheets securely
to a board, as previously described. The burning should be begun at the
lowest point of the seam. After regulating the flame, the point of the
inner flame is applied to the edge of the outer sheet slightly above the
point decided upon as the starting point, and at an angle of about 30
degrees, as shown at _a_ in Fig. 29. As the drop begins to melt it will
have a tendency to flow downward. By a quick turn of the wrist the flame
must then be directed against the back sheet and slightly under the
melting drop.
The under sheet should brighten at once, and the force of the flame,
being partially directed against the melted drop, tends to force it
against the bright spot on the back sheet, with which it instantly
unites. The flame must then be withdrawn for an instant, to give the
fused drop time to set. The operation must be repeated until the seam is
finished. Using ordinary language, it may be said that the drop is cut
from the upper sheet, carried slightly downward and then stuck against
the back sheet by the force of the flame.
[Illustration:
_Fig. 29.—Burning an Upright Lap Seam._
]
This seam is the one most used, and the beginner should practice it
diligently. After mastering it in the position shown in the cut, the
board should be fastened to the floor and the beginner should practice
burning the upright seam from above the work. This position occurs many
times in lining tanks, and the beginner who conquers the upright seam in
that position can consider himself sufficiently proficient to attend to
any job of lead burning that may arise. The beads of lead will appear
more compact and regular than in the flat seam, and if properly done
will upon cutting the sample show a very strong joint.
Inverted Lap Seam.
This seam should be attempted only after becoming very proficient with
the blow pipe and flame, after which it becomes as easy to burn as in
any other position. In order to get the range of the seam the sheets
should be arranged in the position shown in Fig. 27. The burning is
begun on the upright seam, and continued up and over the curved portion
and on to the inverted seam. The graduation from the upright seam to the
inverted seam is simple and gradual, and is hardly noticeable.
After accomplishing the inverted seam in this manner, strips of lead
should be prepared and fastened to the board as described for upright
seams. The board should be supported in an inverted position at a
convenient hight over the operator's head. The flame should be shortened
as much as possible. The burning may be started at any convenient point
and continue in each direction. The point of the inner flame is applied
to the seam at a slight angle, as _a_. The object is to obtain a fusion
between the back sheet and the upper edge of the lap. When this is
accomplished fusion proceeds easily.
[Illustration:
_Fig. 30.—Burning an Inverted Corner Seam._
]
The hardest part of this seam is in starting it, and when once started,
with a little patience and care, the balance of the seam can be fused
without any trouble. Fig. 30 shows an exercise which the beginner should
practice after having conquered Fig. 27, as it teaches the making of an
inverted corner seam. Of course, this position seldom occurs in small
work, but if the burning of it is once accomplished it will give the
operator considerable confidence in his own ability.